Heretofore, a nickel base superalloy has been used for a high-temperature structural member for use in an airplane engine and the like; however, from viewpoints of weight reduction, lifetime improvement, fuel efficiency improvement and the like, a composite material that replaces the nickel base superalloy has been studied, and a ceramic matrix composite (CMC) in which ceramic fiber is cured by ceramics has attracted attention (refer to the following Patent Literature 1).
The ceramic matrix composite is compounded with the ceramic fiber to make up for low ductility, which is a disadvantage thereof, while making use of high heat resistance, high rigidity, high abrasion resistance, high chemical resistance and the like, which are advantages of the ceramics, and the ceramic matrix compound can be used in a much higher-temperature environment that the nickel base superalloy. For the ceramic matrix composite, large improvement of fuel efficiency can be expected (refer to the following Non-Patent Literature 1).
Since this ceramic matrix composite is a difficult-to-cut material, the ceramic matrix composite has heretofore been subjected to surface machining by grinding, it has been difficult to cut/machine the ceramic matrix composite by an end mill, a drill and the like, and a lifetime of each of such tools has also been short. For example, in a case of machining the ceramic matrix composite by a cutting tool or a grindstone, a material removal amount becomes no more than 0.06 cc/min, and continuous machining has been impossible.
As a method for improving a ceramic-based or metal-based difficult-to-machine material such as the ceramic matrix composite, laser-assisted machining is provided. This laser-assisted machining includes: (1) a method of cutting a metal material by irradiating the metal material with pulsed oscillation laser light (refer to the following Patent Literature 2); (2) a method of generating cracks on a surface of a cutting target material and forming an embrittled layer by rapid heating/rapid cooling for a high-hardness material and a high-brittleness material (refer to the following Patent Literature 3); (3) milling by laser assistance (refer to the following Patent Literature 4); and the like.